Propane Enrichment of Biomethane Draft Course Content

Biomethane is methane sourced from renewable biomass such as organic waste, sewage, agricultural residues or energy crops. It can also be derived from woody biomass like forestry residues through production of synthetic gas. In each case it offers a climate friendly way of substituting fossil natural gas and is a flexible energy carrier for fuel, electricity and heat applications, moreover, material use for biomethane offers additional possibilities. Spacial separating the biogas production plant from its point of utilization offers a lot more potential for increase the energy efficiency by serving heat sinks with thermal energy from cogeneration in a biomethane combined heat and power plant (CHP).

Countries like Sweden, The Netherlands, Germany and Switzerland have already gained experience in integrating this environmentally friendly technology into its energy system. Throughout Europe (in 2013) there were in total more than 200 biomethane plants in operation, a fact that clearly shows that gas upgrading technology is mature and proven, thus technology is no longer to be regarded as a restricting factor. Biomethane offers tremendous potential when it is produced and injected into the natural gas grid. The existing natural gas infrastructure can be used for transporting the green gas to its final consumer, where due to its flexibility, biomethane can make a contribution to reducing greenhouse gases (GHG) in all three sectors – electricity, heat and transport. via www.greengasgrids.eu

UK Government Support for Gas-to-Grid Injection

Biomethane injected into the grid and subsequently used for heating and cooking across the country is eligible for regular payments under the government’s non-domestic Renewable Heat Incentive (RHI) scheme. This provides an attractive income stream for AD companies, so it’s easy to see why increasing numbers of purpose-built gas-to-grid plants are cropping up. via https://envirotecmagazine.com/2017/07/10/things-to-know-about-propane-enrichment/

Why is Propane Enrichment of Biomethane (UK) Necessary?

The upgrading of biogas into a commercially viable biomethane offers the opportunity to inject this green energy source back into the national grid. For this to happen the biomethane needs to reach the gas quality standards as set out in the Gas Safety (Management) Regulations 1996. Typically natural gas in the UK grid contains 90% methane, with a calorific value of about 39.5 MJ/m3. Biomethane on its own characteristically has a methane content of up to 98% and a calorific value of 36 MJ/m3. In order to match the two energy sources, biomethane needs to be ‘spiked’ (enriched) with a gas with a higher energy content, such as propane. via www.flogas.co.uk

The enrichment process ensures it has an energy profile that matches that of the natural gas used in the grid.

The UK grants non-discriminatory but not priority grid access for biogenic gases. There are no legal restrictions regarding the sources of biogenic gases meaning that biomethane derived from landfill or sewage gas is also allowed to be injected in to the gas grid. However, there is no renewable incentive for gas from landfill and hence there are no such projects. In the UK the typical gross calorific value is 39.0 – 39.5 MJ / m3 while the heating value of 100 % biomethane is about 37.7 MJ / m3.

Due to the high heating value, significant amounts of propane or LPG are needed to adjust the heating value of the injected biomethane. For historic reasons (related to the fact that UKCS gas has no oxygen) an 0.2% specification for oxygen is in place.

Two main sets of regulations in the UK drive the minimum gas quality requirements for grid injection: the Gas Safety (Management) Regulations and the Gas (Calculation of Thermal Energy) Regulations. These regulations are enforced by HSE and Ofgem respectively. In general the parameters covered by these regulations are not substantially different from those covered elsewhere in Europe. The limit values of these parameters are broadly similar to elsewhere in Europe with the exception of those covering gas interchangeability (and hence the safe operation of gas appliances) and oxygen content.

Should the biogas produced contain significant oxygen then compliance with the oxygen requirements of the GS(M)R may be an issue. Discussions are underway with the HSE to address this issue which arises because the existing UK Oxygen specification of 0.2% was set based on North Sea gas flows. via www.greengasgrids.eu

Lecture 4: How to Enrich Biomethane in Order to Supply Gas-to-Grid

Typically, around 50% of biomethane produced falls below the calorific values demanded by the grid: the Gas Safety (Management) Regulations 1996 (GSMR) require a calorific value (CV) of between 37.5 MJ/m3 to 43.0 MJ/m3. However, blending this lower-grade biomethane with 3-4% of Calor gas is all it takes to meet grid quality requirements.

How it works

1. LPG (propane) is pumped from its storage tank to a vapouriser before being injected into the biomethane at grid entry.

2. The mixture is then odourised (to add the characteristic smell of natural gas) in proportion to the gas flow.

3. The whole process is monitored and controlled by a computer using information from flow meters and gas analysers placed both upstream and downstream.

4. The resulting analysis calculates how much additional LPG (propane) needs to be added.

5. A second gas analyser measures the amount of propane in the blended mix.

6. The final mixture is injected into the grid.

Source:

The preceding section provided by Calor. Calor, is a leading UK supplier of LPG, is a trusted partner for rural businesses looking to sell their excess biogas to the national grid and receive valuable Renewable Heat Incentive payments. Website: www.calor.co.uk/gastogrid

Calorific value: The energy value of a food or fuel, given by the heat evolved when a unit amount (1 gram or 1 kg) is completely burnt in oxygen.

RHI: (Non-Domestic Renewable Heat Incentive) The Non-Domestic Renewable Heat Incentive (RHI) is a UK government environmental programme that provides financial incentives to increase the uptake of renewable heat by businesses, the public sector and non-profit organisations. For approved installations it provides financial support for the installed renewable heat technology for 20 years. They pay-out on a quarterly basis, and aim make payment within 40 working days. via https://www.ofgem.gov.uk/environmental-programmes/non-domestic-rhi

Resources:

A useful pdf which provides the necessary data for those that wish to calculate the heating value of their biogas can be found at the DONETSK STATE TECHNICAL UNIVERSITY websitehttp://masters.donntu.org/2013/fkita/alexandrova/library/Heating_Value_of_Biogas_copy.pdf

A presentation by Prof. Charles Banks, of Southampton University, titled Anaerobic digestion and energy provides information on obtaining calorific data on samples of biogas, using a Bomb Calorimeter to combust a biogas sample and calculate the calorific value from measuring the temperature rise. www.valorgas.soton.ac.uk

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